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Fast, persistent, Ca2+-dependent K+ current controls graded electrical activity in crayfish muscle

AuthorsAraque, Alfonso ; Buño, Washinton
Issue Date1995
CitationPflugers Archiv European Journal of Physiology 430: 541- 551 (1995)
AbstractThe early outward current in opener muscle fibres of crayfish (Procambarus clarkii) was studied using the two-electrode voltage-damp technique. This current was abolished in Ca2+-free and 5 mM Cd2+ solutions, and was blocked by extra- or intracellular tetraethylammonium, indicating that it was a Ca2+-dependent K+ current [I(K(Ca))]. I(K(Ca)) was voltage dependent, apamin insensitive and sensitive to charybdotoxin (CTX), which, in addition to its tetraethylammonium sensitivity, suggests that the channels mediating I(K(Ca)) behave in a BK type manner. I(K(Ca)) activation was extremely fast, reaching a maximum within 5 ms, and the inactivation was incomplete, stabilizing at a persistent steady-state. I(K(Ca)) was insensitive to intracellular ethylenebis(oxonitrilo)tetraacetate (EGTA), but was abolished by injection of the faster Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), suggesting that voltage-dependent Ca2+ channels and those mediating I(K(Ca)) should be clustered closely on the membrane. Under two-electrode current-clamp recording mode, low amplitude, graded responses were evoked under control conditions, whereas repetitive all-or-none spikes were elicited by application of CTX or after loading the cells with BAPTA. We conclude that I(K(Ca)) activates extremely quickly is persistent and is responsible for the generation and control of the low amplitude, graded, active responses of opener muscle fibres.
Identifiersdoi: 10.1007/BF00373891
issn: 0031-6768
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